Studies will continue on structural microheterogeneity of human erythrocyte membrane sialoglycoprotein observed in preparations of individual donors. In one approach differences in structure and properties of three cyanogen bromide fragments are under examination. The 8-10 residue N terminal peptide and the large carbohydrate containing peptide from the middle of the molecule have been isolated in pure form. We plan to devise yet more satisfactory methods for purification of the C terminal peptide, devoid of carbohydrate. Covalent polypeptide and carbohydrate structure of the N terminal peptide will be compared in preparations from individual donors; the C terminal peptide will be characterized as to its amino acid composition and binding properties in regard to the other two peptides. Fragments of the molecule were found to be present in preparations from two individual donors. Another approach involves examination of the sialoglycoproteins from erythrocytes of individual donors for presence of such fragments. Origin of the fragments - whether endogeneously present or rising during preparation of membranes or the sialoglycoproteins will be investigated. Structure of glycopeptides released by trypsin during serial subculturing of calf aortic smooth muscle cells in tissue culture will be examined. Experiments will focus on composition and size of the carbohydrate units and whether fidelity of structure is preserved during serial trypsinizations. Relationship of units to those present in the human membrane sialoglycoprotein will be evaluated.